1. Field of the Invention
The present invention relates to a system for evaluating a semiconductor device.
2. Description of the Related Art
In a prior art system for evaluating a semiconductor device (see JP-A-6-300824), the semiconductor device is irradiated with a visible laser light beam, an electron beam or an ion beam, and thus, an irradiated area of the semiconductor device is heated. As a result, in increase of resistance is caused by the increase of temperature in the semiconductor device to create a current deviation therein. This is called a beam induced resistance change (BIRCH) method. Specifically, an optical beam induced resistance change (OBIRCH) method, an electron beam induced resistance change (EBIRCH) method and an ion beam induced resistance change (IBIRCH) method are named after the BIRCH method, and use a laser beam, an electron beam and an ion beam, respectively. Thus, voids in a interconnect layer such as an aluminum layer and precipitates of silicon can be detected by detecting the above-mentioned current deviation. Also, a current flowing through an interconnect layer of the semiconductor device can be monitored by the above-mentioned current deviation. Thus will be explained later in detail.
In the above-described prior art system, a constant voltage, i.e., a bias voltage is usually applied to the semiconductor device; however, a bias-free or non-bias OBIRCH method (NB-OBIC method) is known (see T. Koyama et al, "Bias-free evaluation technique for Al interconnects with high sensitive OBIC", Proceedings of Japanese Applied Physics Society, 22a-ZP-10, p.586, 1994). In the NB OBIC method, if a fault exists in an interconnect layer, the conduction state of heat is different in the proximity of the fault, so that a temperature gradient is generated in the proximity of the fault, thus generating an electromotive force therein, which can be detected as a current.
In the above-described prior art system, however, if the semiconductor device is irradiated with a laser beam or an electron beam, electron-hole pairs are generated in a semiconductor substrate of the semiconductor device, so that such electron-hole pairs also generate a current therein. This is called an optical beam induced current (OBIC) phenomenon and an electron beam induced current (EBIC) phenomenon for the laser beam and the electron beam, respectively.
For example, in the OBIC phenomenon, an OBIC signal overlaps with an OBIRCH signal (or an NB-OBIC signal). Note that, usually, the OBIC signal is larger than the OBIRCH signal (or the NB-OBIC signal), and in addition, the dynamic range of the system is too small to amplify both of the OBIC signal and the OBIRCH signal (or the NB-OBIC signal). Therefore, the OBIRCH signal (or the NB-OBIC signal) cannot be observed, since the OBIC signal is too strong.
Similarly, in the EBIC phenomenon, an EBIC signal overlaps with an EBIRCH signal (or an NB-EBIC signal). Note that, usually, the EBIC signal is stronger than the EBIRCH signal (or the NB-EBIC signal), and in addition, a dynamic range of the system is too small to amplify both of the EBIC signal and the EBIRCH signal (or the NB-EBIC signal). Therefore, the EBRCH signal (or the NB-EBIC signal) cannot be observed, since the EBIC signal is too strong.
In a test element group (TEG) where test elements are formed in a semiconductor chip for the evaluation of circuit characteristics and manufacturing process characteristics to establish a new manufacturing process or modify a manufacturing process, connections for the test elements can be designed to suppress the OBIC signal or the EBIC signal. However, actual semiconductor products cannot be designed to suppress the OBIC signal or the EBIC signal.
On the other hand, if a semiconductor device is irradiated with an ion beam, an irradiated area of the semiconductor device is sputtered by the ion beam, so that it is impossible to evaluate the semiconductor device non-destructively.